FIG. 9 illustrates an air-conditioning system. As shown in this figure, an air-conditioner 64 comprises a compressor for compressing a gaseous refrigerant (not shown); a condenser 66 for cooling the compressed gaseous refrigerant by cooling water to convert into a liquid refrigerant; and an evaporator into which the liquid refrigerant flows after the pressure of the liquid refrigerant is reduced through an expansion valve (not shown).
The condenser 66 is provided in a cooling tank 70, in order to cool refrigerant flowing inside the condenser 66. A cooling tower 68, which supplies cooling water to the cooling tank 70 through circulation of the cooling water, comprises a cylindrical tower body 72 and a water receiving bath 74 provided below the tower body. The water receiving bath 74 and the cooling tank 70 are connected together via a supply line 76, so that circulation water in the water receiving bath 74 can be transferred to the cooling tank 70.
A filler unit 78 having a plurality of passages, through which circulation water and cooling air flows, is incorporated in the tower body 72. In order to spray the circulation water onto the filler unit 78, a spray nozzle 80 is attached to the tower body 72. The spray nozzle 80 is connected to the cooling tank 70 via a return line 82, whereby the circulation water in the cooling tank 70 can be supplied to the spray nozzle 80 by a circulation pump 84 provided in the supply line 76.
The circulation water sprayed from the spray nozzle 80 onto the filler unit 78 passes through a plurality of passages formed within the filler unit 78, and then falls into the water receiving bath 74. As described above, a circulation water channel for circulating water therethrough is formed from the cooling tower 68, cooling tank 70, supply line 76 and return line 82, wherein the tower and the bath are connected by supply and return lines, and water can flow through the circulation water channel by operating the circulation pump 84.
A blower 86 provided in the tower body 72 creates air flow in the tower body 72, such that the air flow enters at the bottom of the tower body 72 and then flows through the passages within the filler unit 78 in the direction opposite to the flow of the circulation water. This allows the circulation water to be cooled, by heat-exchanging through contact with the circulation water directly with air, as well as by utilizing the evaporative latent heat of the circulation water. In order to refill the reduced circulation water due to evaporation of the circulation water, cooling water is added to the tower body 72 via a refilling line 90, which may be opened or closed by a float 88.
However, circulation water constantly evaporates away from the cooling tower 68, since the cooling tower 68 utilizes the evaporative latent heat of water in order to cool the circulation water for cooling as described above. Tap water and groundwater used as circulation water in the cooling tower 68 often contains metal ions such as calcium, magnesium, and dissolved silica. As described above, the tap water and groundwater is continuously added to the reduced circulation water due to evaporation thereof.
Accordingly, the concentration of metal ions contained in the circulation water will gradually increase. Specifically, tap water having an electrical conductivity of 100 to 200 micro Siemens per centimeter (μS/cm) at the beginning of use, will have an increased conductivity of 1000 μS/cm or more within a few days to a week of operation. The metal ions will then coagulate to form scale, causing a reduction of heat-transferring efficiency by adhering to the heat-exchanging surface of the condenser 66, and an increase of the flow resistance of the cooling water by adhering on the internal surface of piping, through which the circulation water flows.
Further, a large amount of contaminating organisms, such as algae, Legionella bacteria and the like, may grow in the circulation water, and be scattered along with the circulation water in the form of a mist from the cooling tower, causing health problems for people operating around the cooling tower or residing in the vicinity thereof.
To address the problems described above, one measure has been taken in which tap water or groundwater is added to the circulation water to reduce the concentration of metal ions, in order to prevent scale from forming. However, this would disadvantageously increase the cost for circulation water in areas where tap water or groundwater is expensive, and in turn would increase the cost of operating and maintaining of the air-conditioner.
Accordingly, as with the case of business establishments not accessible to low-cost tap water or groundwater, another measure has been taken in which the electric conductivity of the circulation water has been controlled by adding chemicals, so that the adhesion of scale to the heat-exchanging surface of the condenser and the internal surface of piping can be prevented. However, such chemicals have to be added to the circulation water periodically, and result in a higher cost even in this case.
Furthermore, the adhesion of scale to the heat-exchanging surface of the condenser and the internal surface of the piping cannot be completely prevented by adding chemicals to the circulation water. Therefore, the removal of adhered scale, and relating cost and labor are still required, even though the interval removing operation can be extended.
Along with the propagation of algae and bacteria, another measure has been taken in which a biocide is added to the circulation water. However, this cannot suppress the propagation of algae and bacteria in the long term, and the propagated algae and bacteria may be spread into the air from the cooling tower, along with the biocide and the like, causing air pollution.
In order to solve the above described problems, a wide variety of cleaning devices capable of electrically removing metal ions from circulation water by electrolysis have been proposed, as described in Japanese unexamined patent publication Nos. 2001-259690, 4-18982, 61-181591, 58-35400, 2001-137891, 9-103797, 2001-137858, 9-38668, 11-114335, etc.
One example of such a cleaning device, a cleaning device comprising an electrode plate unit having electrode plates placed in a face-to-face manner between one another; and an electrolysis cleaning tank having the electrode plate unit therein, wherein circulation water is introduced to the electrolysis cleaning tank, and positive and negative voltage is applied to the electrode plates, thereby allowing metal ions contained in the circulation water to be precipitated on the surface of the negative electrode plates in the form of scale, and thus removing metal ions from the circulation water, has been proposed.    Reference 1: Japanese unexamined patent publication No. 2001-259690    Reference 2: Japanese unexamined patent publication No. 4-18982    Reference 3: Japanese unexamined patent publication No. 61-181591    Reference 4: Japanese unexamined patent publication No. 58-35400    Reference 5: Japanese unexamined patent publication No. 2001-137891    Reference 6: Japanese unexamined patent publication No. 9-103797    Reference 7: Japanese unexamined patent publication No. 2001-137858    Reference 8: Japanese unexamined patent publication No. 9-38668    Reference 9: Japanese unexamined patent publication No. 11-114335